The invention relates to measuring apparatus for engine ignition systems and more particularly relates to apparatus for measuring the dwell angle of an ignition system.
Dwell measuring apparatus includes electrical circuitry composed of a plurality of electrical components interconnected for producing a desired dwell measurement function. For example, U.S. Pat. No. 4,092,584, issued to Richard A. Karlin, on May 30, 1978, and assigned to the same assignee as the present invention, discloses a dwell measuring apparatus in which resistors, diodes, an inductor, a capacitor and a transistor, are inter-connected to provide an output signal to a dwell meter for indicating the dwell angle of an automotive engine ignition system.
Due to manufacturing and cost requirements, electrical components are made within certain tolerance ranges, and therefore, electrical apparatus will include several potentiometers (variable resistors) which are manually tuned to calibrate the electrical apparatus during manufacture thereof.
However, potentiometers are relatively expensive, as is the labor in tuning each potentiometer. In dwell measurement circuitries having the capability of testing more than one cylinder-type engine, for example, 4 cylinder, 6 cylinder and 8 cylinder engines, usually three potentiometers are required, one for each engine type. Thus, it would be highly desirable to devise an electrical dwell measuring circuitry capable of measuring the three most popular cylinder-type engines while needing only one calibration potentiometer.
Further, it would be desirable if such a dwell measurement circuitry would not depend on a points-closed signal of zero volts. That is, many prior art measuring circuits are based on the principle that when the points are closed, the ignition signal is zero. However, with the advent of modern semiconductor components to perform the switching function, a non-zero points-closed voltage occurs in some of the new semiconductor ignition systems, as for example, General Motors Corporation High Energy Ignition System.